Lansing — The Michigan Capitol was partially evacuated Tuesday and neighboring buildings cleared as a state police bomb squad investigated a suspicious package left in a U.S. Post Office drop box.

But there was no bomb, said Sgt. Todd Johnson of the Lansing Police Department, which was called in at around 1 p.m. after a backpack was found in the drop box outside the Charles E. Chamberlain Federal Building at the corner of Allegan and Townsend streets southwest of the Michigan Capitol.

"We brought one of our special dogs down here, and it did find the possibility of some gun power residue," Johnson said. "So at that point, we obviously considered it a threat, blocked off a large area down here and called in the Michigan State Police bomb squad to make sure it was not a bomb."

Authorities evacuated the federal building, the Senate Office Building and asked state senators, staff and media to leave the south side of the Michigan Capitol at around 1:45 p.m. The "all clear" for them to return to work was given around 2:20 p.m.

Several senators, staff, lobbyists and members of the general public gathered inside the Boji Tower building east across the street from the Capitol during the partial closure.

“They called a code red and asked everybody to leave,” said state Sen. Mike Kowall, R-White Lake. “So I just got my staff out of there.”

“That the first time that’s happened in all the years I’ve been here,” said Kowall, who has served in the state Senate the past eight years and previously spent four years in the state House.

A state police bomb squad robot investigated the backpack but did not detonate it, Johnson said.

"They had an X-ray machine," he told reporters. "It looked like there was no mechanical parts. ... It looked like personal belongings and the reason it's in the post office box, I have no idea."

The post office empties the mail box most evenings, Johnson said, and Lansing police may try to obtain security footage from a neighboring building as they continue to investigate the origins of the backpack.